The objective of the proposed research is to investigate the anatomical basis for binaural hearing in insectivores and prosimian primates. The purpose of these comparative observations is to: (1) provide data relevant to the evolution of hearing in primates and (2) provide an anatomical basis for behavioral studies on binaural hearing and auditory localization. In the anatomical studies, modern techniques for demonstrating connectivity in the nervous system are used to show ascending projections from the cochlear nucleus and superior olivary complex to inferior colliculus and descending connections from auditory cortex to inferior colliculus. The results of these anatomical experiments have provided specific hypotheses about the function of various parts of the central auditory system. Some of these hypotheses will be tested in behavioral experiments by examining the effects of lesions in subdivisions of the auditory pathway on auditory discriminations, especially localization of sound in space. BIBLIOGRAPHIC REFERENCES: Casseday, J.H., and Neff, W.D. Auditory localization: role of auditory pathways in brainstem of the cat. J. Neurophysiol., 1975, 38:842-858. Neff, W.D., Diamond, I.T., and Casseday, J.H. Behavioral studies of auditory discrimination. In: Keidel, W.D. and Neff, W.D. (Eds), Handbook of Sensory Physiology, Vol. V/1, Berlin-Heidelberg, New York: Springer, 1975, pp. 307-400.